The present invention relates to a communication system, a communication control method and a communication control apparatus for performing communication by wireless between a radio terminal and a network.
In recent years, mobile radio communication services spread and a word xe2x80x9cmobile computingxe2x80x9d also has taken root in general. A mobile computation being in wide use at the present time is performed by connecting a personal computer through an adapter to a portable telephone subscribing to a mobile radio communication service. FIG. 11 shows an embodiment of a communication system in which a mobile computation of this kind is performed.
In FIG. 11, 1-1 designates a mobile station for performing a mobile computation, and is composed of a personal computer 1a, a radio terminal 1b, and an adapter 1c for connecting both of them with each other. The radio terminal 1b designates a radio terminal subscribing to a mobile radio communication network service, and is a portable telephone for example.
2-1 to 2-h designate base stations of a mobile radio communication network, and each of them performs communication through a radio channel with the radio terminal 1b. 3 designates a mobile radio communication switching control means having a function as a mobile radio communication switching station and a function as a mobile radio communication control station. 4 designates a public network. The mobile radio communication switching control means 3 is connected with this public network. 5 designates a LAN of a corporation for example and is connected with the public network 4.
In the configuration described above, when a user originates a call from the personal computer 1a through the radio terminal 1b to a desired service access point, a radio channel is established between the radio terminal 1b and one of the base stations 2-1 to 2-h under control of the mobile radio communication switching control means 3, and a channel for linking the base station and the desired service access point with each other is established. Using a communication channel thus established, the user can receive an information providing service from a provider through the public network 4 by means of the personal computer 1a, and can access a LAN 5 of a corporation. In this case, the radio terminal 1b provides a function as a modem for performing a radio communication with the base station to the personal computer 1a. 
Furthermore, a system is utilized in which a mobile station can be connected with a LAN or an Internet provider by accessing an interface to a network operator, and can receive an information service from a LAN and the like by means of packet transfer through a radio channel and the system is based on the same principle as the configuration shown in FIG. 11. A system of this kind is disclosed by, for example, pp.6 to 9 of xe2x80x9cNTT DoCoMo Technical Journalxe2x80x9d, July 1997 issued by NTT Mobile Communication Network, Inc.
Thanks to such technologies as described above, a mobile radio communication service which has mainly provided voice communication services up to now is evolving to a service supporting not only data communication, particularly such data communication by telephone connection as a personal computer communication but also a LAN connection.
It is thought that technologies utilizing a mobile radio communication network will develop to a radio LAN taken in a broad sense in which radio terminals can be connected with each other through a radio channel and can freely move over a wide area.
In the future, however, in case of attempting to provide various communication services (data communications, voice communications and the like) utilizing such a mobile radio communication network as described above, the following problems will happen.
(1) Since a communication channel between a mobile station and a desired service access point includes a radio channel, in case that the radio channel is not good or the mobile station is not within the radio service zone of a base station, the mobile station cannot receive a communication service. In such a case, if a mobile station is within the sphere of daily action, a user can find out a communicable area and take a measure such as performing communication within the area or the like. However, when a user is moving by car or train, such a measure cannot be taken.
(2) Particularly, when a user inside a high-speed mobile object such as a train on the Shinkansen Line or the like attempts to perform a data communication, a circuit interruption is frequently caused during communication by influence of tunnels or opencuts. Therefore, it is not possible to provide efficient and user-friendly services.
(3) Furthermore, when a circuit interruption occurs frequently as described above and the number of incompleted calls is increased, an overhead operation for connecting a call becomes useless as a result, and the efficiency of a communication system is lowered.
(4) In order to build such a radio LAN taken in a wide sense as described above, it is necessary to always make an original LAN environment capable of being used as it is at a place to which a terminal (a radio terminal or a mobile station in this case) has moved even in case that each of terminals moves over a wide area. However, since a former technology utilizing a mobile radio communication network is insufficient in agent functions, it is difficult to make each radio terminal always utilize an original LAN environment at a place to which the radio terminal has moved.
The present invention is based on the consideration of such circumstances as described above, and an object of the present invention is to provide a communication system, a communication control method and a communication control apparatus which can provide a user-friendly communication service to a radio terminal user even under a poor communication environment.
In order to attain such an object, a communication system according to the present invention disposes a communication control apparatus between a radio terminal and a network side. In a preferable embodiment, each radio terminal is carried into a mobile object and a communication control apparatus is arranged in advance in such a mobile object.
A communication control apparatus relays the exchange of information between a radio terminal and a network by performing a radio communication with the radio terminal and by performing a radio communication with a base station.
The communication control apparatus is provided with a communication control server for performing a radio channel control between it and a radio terminal and for performing a radio channel control between it and a base station, and a communication unit for performing a radio communication with a radio terminal and a radio communication with a base station using radio channels established by the communication control server.
Main control functions included in channel control functions provided by the communication control server are as follows:
In case that a communication control server has received a communication request from a radio terminal and the server cannot rapidly establish a radio channel between it and the base station in response to the communication request, the server transmits a notification indicating to reject the communication request to the radio terminal.
In another embodiment, in case that a communication control server has received a communication request from a radio terminal and the server cannot rapidly establish a radio channel between it and the base station in response to the communication request, the server reserves the communication request. The server starts communication between the radio terminal and the network side when the server has established the radio channel. That is to say, in case that the server cannot provide a real time communication requested by a user, it provides an alternative means as the second best measure.
In a further other embodiment, in case that a communication control server has received a communication request from a radio terminal and the server cannot rapidly establish a radio channel between it and the base station in response to the communication request, the server sends a packet transmission request to the radio terminal. When a packet has been transmitted from the radio terminal, the server stores the packet. The server transmits the packets thus stored to the network when it has established the radio channel between it the base station.
Additionally to these, a communication server provides to a radio terminal such various agent functions as a control function and the like in case that it has received communication requests of plural kinds being different in priority from one another from radio terminals.
According to the present invention, since a communication control apparatus performs a channel control between it and a network side instead of a radio terminal, load on the radio terminal side is lightened. Furthermore, it is possible to provide a user-friendly communication service in which a communication state between a radio terminal and a network side is hidden to a user of each radio terminal by means of agent functions provided in the communication control apparatus.